Synaptic strength must be regulated in the face of changing levels of input in order to ensure that total strength I of all inputs are controlled so as to maintain output finng within reasonable limits and these mechanisms must I work in conjunction with mechanisms of synaptic plasticity. Its clinical importance can be best illustrated by the I condition of epilepsy where these mechanisms are disrupted at the extreme. The association of epilepsy with l numerous forms of inherited disorders of cognitive function such as Fragile X and Down Syndrome and the l increasing use of anti-epileptic drugs for the treatment of mood disorders highlight the importance or-thesel mechanisms in maintaimng normal brain function. This grant proposes to study the underlyingmechanisms by l which synaptic- adaptation is achieved in the face of changing levels of input and the effects ot this adaptation I on plasticity, building on recent progress in the lab. The first two parts will use strategies to describe morel completely the signaling events in the pathway from synaptic input to synaptic modification, taking advantage I of the ease of manipulation and measurement in the primary culture system. This part of the study will begin I with a careful dissection of the sources of electrical input and calcium entry responsible for the induction ot the I key signaling events, followed by an elucidation of the mechanisms of regulation of key intermedia_ signaling ] products, examining the regulation of their enzymatic activity, stability, transcription, translation and transport I to the synapse. In addition, a more complete description of the signaling cascade will be drawn out trom l microarray studies comparing results from disruption of the signaling pathway at various points. The next part l of the study will look closely at the microphysiology of this phenomenon (a) to elucidate the elements ofl adapation that are cell-autonomous, by comparing effects of network changes and manipulations !n only one I cell (b) to describe adaptive changes at the level of single synapses, and (c) to determine the pre- or l postsynaptic locus of induction of the various elements of adaptation. These studies will take advantage of long / standing expertise in the lab in studying the physiology of single synapses involving focal stimulation and t measurement of synaptic responses at unitary sites. The Iast part of the project will apply the knowledge gained I in the previous sections to try to understand the impact of adaptation m intact hippocampal circuits, using the I organotypic slice culture. Primary questions addressed will be differences in the expression of adaptation at two 1 different sets of afferents and consequences of this adaptation on the induction and expression of LTP. We will I look for forms of LTP not previously found in pyrmnidal neurons and for changes in the performance of/ preexisting mechanisms of LTP. [ =ERFORMANCE SITE(S) (organization, city,state) Stanford University, Stanford CA KEY PERSONNEL. See instructions on Page 11. Use Name TSIEN, Richard W. LINDSKOG, Maria THIAGARAJAN, Tara WHEELER, Damian G. continuationpages as neededfo providethe required Organization STANFORD UNIVERSITY STANFORD UNIVERSITY STANFORD UNIVERSITY STANFORD UNIVERSITY PHS 398 (Rev 4/98) Page 2 . Number pages consecutively at the bottom throughoutthe appliootion. Do not u=_suffixessucn as3a, 3b. information in the format shown below. Role on Project P.I. Postdoctoral fellow Postdoctoral fellow Postdoctoral fellow BB CC Principal Investigator/Program Director (Last, first, middle): Tsien, Richard W. Type the name of the principalinvestigator/programdirector at the top of each pdnted page and each continuationpage. (For type specifications, see instructionson page 6.) RESEARCH GRANT TABLE OF CONTENTS Page Numbers Face Page ........................................................................................................................................................................................................ Description,